The field of the invention is sediment traps, particularly sediment traps for culverts.
The term “culvert” is used herein to mean a conduit used to enclose, contain, and direct a flowing liquid, generally surface run-off water. In situations where end-pieces are employed, the term “culvert” includes the end pieces. It is to be understood that culverts are used herein as an exemplary and valuable application of the invention but that the scope of the invention goes beyond culverts and run-off water, as will be evident by this disclosure.
Normally culverts are used to provide a passageway for water to pass underneath a road, railway, embankment, or other man-made structure placed across the natural path of the water. Thus, the culvert protects the structure from washout and prevents flooding.
Culverts may have any of a variety of shapes in cross-section, but round and oval shapes predominate. Although the embodiments of the invention presented herein show round or oval culverts, the invention is equally and easily adapted to culverts of any shape. Typically culverts are made of concrete, metal, or synthetic materials. The present invention is applicable to culverts made of any material.
Culverts have an inlet and an outlet, the openings through which the water enters and exits the culvert, respectively. Often these inlets and outlets are produced separately as specially designed and molded “end pieces.” The end pieces are then attached to the conduit when the culvert is put in place. Because a simple round pipe placed in the path of flowing water does not efficiently channel the water into the pipe, culvert inlets and end pieces are often flared to act as a funnel. Such funneled or flared inlets can create a venturi effect in high water flows whereby the velocity of the water is at a maximum as the water is funneled into the body of the conduit. The water velocity then decreases inside the culvert, which causes problems.
Culverts are normally straight and sloped downwards in the downstream direction in order to insure afflux of the water from the inlet to the outlet and thereby minimize slowing or standing of the water while inside the culvert. But in some situations it is necessary to have one or more curves along the length of the conduit, and sometimes culverts, particularly those made of plastics, develop a “belly.” Such bellies also cause problems.
Typically, because of resistance of the walls of the culvert, a venturi effect at the inlet, curves, bellying, etc, the velocity of flow of water decreases inside the culvert. This is problematic because it promotes the settling out of sediments inside the pipe where the sediments are difficult to reach and remove. This process of depositing sediments is referred to herein as “sedimentation.”
As the sediment accumulates within the culvert, particularly under low-flow conditions, water flow becomes restricted and the water pools and backs up inside the culvert, which promotes even faster sedimentation inside the culvert. The sediment may eventually dry out to form a solid mass. Vegetation may begin to grow in the sediment, in which case the roots hold the sediment together. Consequently, when subsequent storm flow occurs, the culvert may be too occluded to handle the flow. Under such conditions, the water backs up and flooding occurs, often damaging the roadway or other structure the culvert was installed to protect. An entire roadway can be washed away in flood conditions because the underlying culvert is unable to handle the full flood flow for which it was initially designed. This causes very significant loss of property and also puts lives at risk.
Of course, the removal of sediment from far inside a culvert is much more difficult and costly than removal of sediment right at the inlet. Given that there are hundreds of thousands of culverts within the United States, the cost of periodic removal of sediment from inside culverts is enormous—to both the private sector and public sector. Large culverts must often be drilled or reamed out; small culverts often need to be replaced entirely. Consequently, the prevention of sedimentation of culverts is preferred over the removal of sediment and there is a strong demand for effective and inexpensive ways to prevent sedimentation from occurring within culverts, which is what the present invention does.